A peristaltic dosing pumps system will eliminate all off-gas concerns. I am using peristaltic pumps since 3 years and the only problem is changing the tube once a year(3-4 minutes) but it is cheap comparing to all the problems you may have with diaphragm pumps.
Almost all UV's are equal regarding performance but quality is different from one to another. I like to work with Sterilight products (www.r-can.com). Using UV necessitate a good water quality: Max. level: Fe = .3 ppm, Mn=.05 ppm, hardness=7 gpg, low turbidity, low color and high UV...
Few chemicals are very effective to treat that effluent. There is few options I suggest:
AquaPerl by Atlas environmental products (819-565-9688) and obtained >98% Zn reduction with that.
Global Ionix system: www.globalionix.com
Moonstone RSA: www.moonstoneinc.ca
Good luck!
Magnetic device will not help. Depending the pH, flow rate and iron level and form. You may use filters like birm, catalox, KDF-85, greensand plus (combined with chlorine injection or KMnO4) or ion exchange.
You may also install a sedimentation tank and pump the supernatant back to filters. Oxidized Mn is easily settleable. And then only purge the sediment to a bag filter.
If you are not allowed to discharge any liquid concentrate you will have to use filtration and bag filtration is the cheapest solution I know. Instead of using GAC cartridges, I suggest Carbon block cartridges, they have an higher filtration capacity.
Instead of non-proven electronic device, I suggest Filtersorb SP. It is an efficient no salt system than can remove hardness EFFECT. See that article for another similar product. Those products have been validated by well recognized...